The present invention relates to a belted radial tire for heavy duty use such as truck/bus tires, in which uneven wear of the tread between the tread crown and tread shoulder is effectively reduced without deteriorating high-speed durability.
In a heavy duty radial tire which is provided radially outward of the radial carcass with a stiff belt made of steel cords, the tread is liable to wear unevenly between the tread crown and the tread shoulder. That is, as shown in FIG. 8, so called shoulder wear (M) is liable to occur. The main cause of such uneven wear has been known to be an uneven ground pressure distribution, and the cause of such uneven distribution is known to be a small radius of curvature of the tread profile. As shown in FIGS. 7(A) and 7(B), when the tread radius is small, the ground pressure is higher in the tread crown than the tread shoulder, and the amount of slip against the ground becomes larger in the tread shoulder. As a result, shoulder wear is caused.
In order to even the ground pressure distribution, heretofore, the tread radius has been increased so as to provide a flat tread profile by increasing the tread rubber thickness in the tread shoulder.
In this method, however, it is very difficult to control the ground pressure distribution, and the ground pressure is liable to increase in the tread shoulder as shown in FIGS. 6(A) and 6(B), which again results in uneven wear. Further, because of the increased rubber thickness, heat generation increases in the tread shoulder, which induces a belt ply edge separation from the surrounding rubber and decreases high speed durability.
On the other hand, truck/bus tires are often reused by being retreaded. In a general retreading process, the worn tread rubber is removed automatically along a programmed curvature or a convex profile by machinery. Therefore, if a tire having a belt of which edges are radially outwardly curved is included, the belt of such a tire is damaged, and the yield of retreading is decreased. Thus, such a truck/bus tire must be designed paying attention to the yield of retreading.